Apologies for the list spam, but there appears to have been several people who have been hit by this.
If you are having problems sending in a review using the 'git review' command after the upgrade and see a line that looks like:
! [remote rejected] HEAD -> refs/publish/master (prohibited by Gerrit: not permitted: create)
You will need to upgrade your 'git-review' python package by running:
sudo pip install git-review
This should upgrade you to version 1.28.0, which you can verify by running:
git review --version
If you would prefer to manually push changes, please be aware that backwards compatibility for pushing changes to "refs/publish/<branchname>" has been removed in 3.0 and instead of giving a warning it will refuse with the error message above. Instead you should use "refs/for/<branchname>"
Thank you to everyone who has reported the issue,